Comparative feeding ecology of two herbivorous damselfishes (Pomacentridae: Teleostei) from the Gulf of California,Mexico

Two species of benthic damselfishes from the Gulf of California, Mexico, use contrasting behaviors when feeding on benthic algal communities. The small (±70 g) Cortez damselfish, Eupomacentrus rectifraenum (Gill, 1862), feeds selectively from a multi-species algal mat, eats fleshy red and green algae and ignores brown and calcareous algae. The giant blue damselfish, Microspathodon dorsalis (Gill, 1862), is a large (±450 g), lethargic, nonselective feeder which grazes on a near monoculture of a fleshy red alga, Polysiphonia sp. Feeding activity for both species is low in the morning peaks during late afternoon, and drops sharply as night approaches. Based on feeding rates, gut-filling times, and weights of gut contents, Cortez damselfish process six to eight full guts of food and giant blue damselfish three full guts of food per day. The algal mat exhibits high standing crops (291–618 g dry wt · m^?2) and low productivity, but the preferred food of the Cortez damselfish (Ulva) appears to colonize the mat frequently and grow rapidly. The Polysiphonia dominated community on giant blue damselfish territories exhibits low standing crops (23 g · m^?2) and high productivity (34–47 times that of the mat per gram algae). Even though the feeding behaviors and resources used by the two damselfishes differ, both species eat similar food (delicate red and green fleshy algae, and depend on rapid colonization and/or high productivity to maintain their primary foods in the grazed algal community.     

Growth of Heterotrophic Bacteria and Algal Extracellular Products in Oligotrophic Waters

The unexpected observation of 200 to 400 coliform bacteria per 100 ml in an unpolluted pristine stream was studied within Grand Teton National Park, Wyo. The high numbers of waterborne bacteria occurred in mid- to late summer at a location where there was a coincidental bloom of an algal mat community. Periphyton samplers were used to measure the algal growth that coincided with the increase in number of bacteria. Laboratory studies followed the growth of various coliform bacteria in the supernatant obtained from a Chlorella culture isolated from the mat community. Mixed natural bacterial populations from the stream and pure cultures of water-isolated fecal and nonfecal coliforms increased by two to three orders of magnitude at 13°C when grown in the algal supernatant. Radioactive algal products were obtained by feeding an axenic Chlorella culture ¹⁴C-labeled bicarbonate under laboratory cultivation at 13°C with illumination. Radioactive organic material from the algae became incorporated into the particulate fraction of pure cultures of coliform bacteria as they reproduced and was later released as they died.     

Effect of larval fish and nutrient enrichment on plankton dynamics in experimental ponds

The hypotheses that larval fish density may potentially affect phytoplankton abundance through regulating zooplankton community structure, and that fish effect may also depend on nutrient levels were tested experimentally in ponds with three densities of larval walleye, Stizostedion vitreum (0, 25, and 50 fish m^–3), and two fertilizer types (inorganic vs organic fertilizer). A significant negative relationship between larval fish density and large zooplankton abundance was observed despite fertilizer types. Larval walleye significantly reduced the abundances of Daphnia, Bosmina, and Diaptomus but enhanced the abundance of various rotifer species (Brachionus, Polyarthra, and Keratella). When fish predation was excluded, Daphnia became dominant, but Daphnia grazing did not significantly suppress blue-green algae. Clearly, larval fish can be an important regulator for zooplankton community. Algal composition and abundance were affected more by fertilizer type than by fish density. Inorganic fertilizer with a high N:P ratio (20:1) enhanced blue-green algal blooms, while organic fertilizer with a lower N:P ratio (10:1) suppressed the abundance of blue-green algae. This result may be attributed to the high density of blue-green algae at the beginning of the experiment and the fertilizer type. Our data suggest that continuous release of nutrients from suspended organic fertilizer at a low rate may discourage the development of blue-green algae. Nutrient inputs at a low N:P ratio do not necessarily result in the dominance of blue-green algae.     

BLUE-GREEN ALGAL MATS IN A SMALL STREAM1

Bedrock erosional features in a small stream (Little Schultz Creek, Bibb County, Alabama) created a variety of habitats for epilithic growth. One suck habitat was illustrated by the occurrence of small falls (<0.3 m) in the main channel of the stream and blue-green algal mats associated with them. The cohesive, laminar algal mats were found at 15 such sites along a 250-m reach of the stream. The primary mat matrix consisted of the blue-green alga Oscillatoria submembranacea Ardissone and Strafforella. The uppermost portion of each mat consisted of a thin (<1 mm thick) green layer of biologically active filaments. The lower layers were thicker (up to 2 cm thick) and consisted of brown laminae of Oscillatoria filaments, and associated sediments. In addition, numerous diatoms mere associated with the mat surface. Some were loosely attached (e.g. Achnanthes); others (Cymbella tumida (Bréb.) V. H.) were stalked. These mats were present throughout the year and showed a bimodal annual distribution with maxima hi February and July. In February, total mat coverage was higher than in July. This winter maximum may have been related to a mode of growth dependent upon sedimentation from storm events and subsequent upward growth of the alga. Mat primary productivity on an areal basis (432 mg C · m^?2· d^?1 in March and 907 mg C · M^?2· d^?1 in April) was 2–12 times the maxima measured on epizoic and cobbles surfaces and other bedrock surfaces in the same stream. The limited areal coverage of the mats, when compared to other surfaces available for algal colonization, made them less important than other epilithic and epizoic surfaces in terms of total primary production in this stream reach. However, we propose that the combination of their unique structure and high primary productivity may make these algal mats sites of high algal and bacterial metabolic activity, which may include anaerobic processes in midchannel, where such activity would not be expected to occur.     

Water chemistry and algal vegetation of streams in the Asir Mountains,Saudi Arabia

Surveys of water chemistry and algal vegetation at nine stream sites in the Asir Mountains, Saudi Arabia, were made in March, 1984. The waters were moderately to highly calcareous with a relatively high Mg: Ca ratio and high concentrations of reactive-Si (x = 12.2 mg l^–1) and F (x = 0.73 mg l^–1). Ammonia typically constituted about one-sixth of the inorganic nitrogen. Filamentous algae (Cladophora and/or Spirogyra) were abundant at all but one site. However two sites, Wadi Habaqah and Al Tanoumah, differed considerably from the others in their overall floristic composition, with various species of Rivulariaceae, Nostoc verrucosum, Schizothrix lardacea and certain other blue-green algae present only here. With one minor exception, heterocystous blue-green algae were absent at the other sites. Tufa was deposited at these two sites, but not elsewhere. Species which appeared to play an active role in calcification included Dichothrix gypsophila, Calothrix parietina, Cladophora glomerata and the moss Bryum sp. A community apparently not previously recorded in the literature was abundant at Wadi Habaqah. This consisted of thick mats of Cladophora glomerata, with a thin surface layer of Zygnemales and numerous colonies of Nostoc verrucosum inside, or towards the underside, of the mat.     

Effects of No. 2 Fuel Oil, Nigerian Crude Oil, and Used Crankcase Oil on Attached Algal Communities: Acute and Chronic Toxicity of Water-Soluble Constituents

Water extracts of a no. 2 fuel oil, a Nigerian crude oil, and used crankcase oil were examined for their effects on algal communities in experiments lasting several weeks conducted under near-natural conditions. No. 2 fuel oil extracts depressed algal biomass (chlorophyll a) and resulted in blue-green algal (cyanobacterial) dominance and decreased diatom occurrence. Changes in concentrations of chlorophyll c, which was specific for diatoms in this work, and phycocyanin, which was specific for blue-green algae, confirmed the observations. Used crankcase oil extracts also depressed biomass, but Nigerian crude extracts did not, and both these extracts had less effect on community composition than did no. 2 fuel oil extracts. Photosynthetic ¹⁴C incorporation was both stimulated and depressed by exposure to extracts with hydrocarbon concentrations 0.038 to 0.124 mg/liter. Short-term exposure to higher concentrations (1.17 to 15.30 mg of hydrocarbons per liter) of no. 2 fuel oil extracts depressed photosynthetic ¹⁴C incorporation by Vaucheria-dominated communities in all tests but one. Toxicity was greater from extracts prepared in the light than from extracts prepared in the dark.     

Aliphatic Hydrocarbons and Fatty Acids of Some Marine and Freshwater Microorganisms

Gas chromatography and combined gas chromatography-mass spectrometry have been used to study the fatty acids and hydrocarbons of a bacterium from the Pacific Ocean, Vibrio marinus, a freshwater blue-green alga, Anacystis nidulans, and algal mat communities from the Gulf of Mexico. Both types of microorganisms (bacteria and algae) showed relatively simple hydrocarbon and fatty acid patterns, the hydrocarbons predominating in the region of C-17 and the fatty acids in the range of C-14 to C-18. The patterns of V. marinus were more comparable to those of the algal populations than to patterns reported for other bacteria. An incomplete correlation between fatty acids and hydrocarbons in both types of organisms was observed, making it difficult to accept the concept that the biosynthesis of hydrocarbons follows a simple fatty acid decarboxylation process.     

Decomposition of Blue-Green Algal (Cyanobacterial) Blooms in Lake Mendota, Wisconsin

Decomposition of natural populations of Lake Mendota phytoplankton dominated by blue-green algae (cyanobacteria) was monitored by using oxygen uptake and disappearance of chlorophyll, algal volume (fluorescence microscopy), particulate protein, particulate organic carbon, and photosynthetic ability (¹⁴CO₂ up-take). In some experiments, decomposition of ¹⁴C-labeled axenic cultures of Anabaena sp. was also measured. In addition to decomposition, mineralization of inorganic nitrogen and phosphorus were followed in some experiments. Decomposition could be described as a first-order process, and the rate of decomposition was similar to that found by others using pure cultures of eucaryotic algae. Nitrogen and phosphorus never limited the decomposition process, even when the lake water was severely limited in soluble forms of these nutrients. This suggests that the bacteria responsible for decomposition can obtain all of their key nutrients for growth from the blue-green algal cells. Filtration of lake water through plankton netting that removed up to 90% of the algal biomass usually did not cause a similar decrease in oxygen demand, suggesting that most of the particulate organic matter used for respiration of the decomposing bacteria was in a small-particle fraction. Short-term oxygen demand correlated well with the particulate chlorophyll concentration of the sample, and a relationship was derived that could be used to predict community respiration of the lake from chlorophyll concentration. Kinetic analysis showed that not all analyzed components disappeared at the same rate during the decomposition process. The relative rates of decrease of the measured parameters were as follows: photosynthetic ability > algal volume > particulate chlorophyll > particulate protein. Decomposition of ¹⁴C-labeled Anabaena occurred at similar rates with aerobic epilimnetic water and with anaerobic sediment, but was considerably slower with anaerobic hypolimnetic water. Of the various genera present in the lake, Aphanizomenon and Anabaena were more sensitive to decomposition than was Microcystis. In addition to providing a general picture of the decomposition process, the present work relates to other work on sedimentation to provide a detailed picture of the fate of blue-green algal biomass in a eutrophic lake ecosystem.     

Ecology of yellowstone thermal effluent systems: Intersects of blue-green algae,grazing flies (Paracoenia,Ephydridae) and water mites (Partnuniella,Hydrachnellae)

Summary As subjects for ecosystem studies, thermal spring effluents offer the advantages of trophic diversity with taxonomic simplicity, ease of sampling, replicability, world-wide distribution and manipulability. The dominant primary producers (filamentous blue-green algae) are grazed by ephydrid flies. These in turn harbor larvae of the water mite Partnuniella. The high instrinic rate of increase of the fly enables it to exploit temporary cool spots in the mat. The lower fecundity and longer life cycle of the mite restrict its ability to exploit temporarily suitable habitat. Thus the intersect of mites with flies is a sensitive measure of stability in the algal mat. Springs with a variable-flow pattern and consequent mat instability had both a lower mean incidence of parasitism and a lower mean larval load per fly. The data support our hypothesis that the abundance and relative densities of organisms in higher trophic levels can be predicted from knowledge of the growth and stability patterns of the filamentous blue-green algal mat in thermal spring effluents.     

Dynamics of benthic algal vegetation and environment in Dutch estuarine salt marshes studied by means of permanent quadrats

Summary Knowledge of the spatial structure of benthic algal vegetations in salt marshes, consisting of about 100 species of blue-green, green, brown and red algae, formed the basis of a detailed study into the dynamics of the algal mat.The temporal changes in algal vegetations and concomitant processes in their environment were studied in 27 permanent quadrats (PQs), plotted in tidal salt marshes and along brackish inland waters in the SW Netherlands. Once a month vegetation and environment of the PQs were examined over the period March 1968-February 1971. From the Spearman rank-correlation between vegetational and environmental parameters it appeared that in semiterrestrial and terrestrial environments the average number of algal species in a relevé and the average similarity between the species composition of successive relevés obtained from one PQ have a significant positive correlation with the stability of the substrate, and hardly any correlation with fluetuations in soil-moisture content and salinity of the soil moisture and with the maximum cover percentage of the phanerogams.Stable substrates tend to bear stable algal mats, as appeared from quantitative data. Small and moderate fluctuations in soil-moisture content and salinity of the soil moisture have no limiting influence on the algal cover degree. During periods of extremely high salinity and concomitant extremely low soil-moisture contents that coincide with evaporation surpluses, the green algal mat bleaches and decreases in cover in semi-terrestrial and terrestrial environments. Below 20% the soil-moisture content is limiting for the expansion of a mat of green algae (Rhizoclonium riparium, Percursaria percursa, Enteromorpha torta, E. prolifera) and Vaucheria species. The mat desiceates and bleaches but recovers after increase of the soil-moisture content above 20% within one month. Two weeks of severe frost (temperature down to – 10°C) do not influence the cover degree of the algal mat in aquatic branckish PQs, but the cover degree in semi-terrestrial PQs decreases. Short lasting soil-moisture salinities of 130–190 Cl^– have no limiting effect on the expansion of the algal mat.Nomenclature authorities are given in Table 3.Contribution to the Symposium of the Working Group for Succession Research on Permanent Plots, held at Yerseke, The Netherlands, October 1975.Communication No. 163 of the Delta Institute for Hydrobiological Research, Yerseke.     

Productivity and species composition of algal mat communities exposed to a fluctuating thermal regime

Algal mat communities growing in thermal effluents of production nuclear reactors at the Savannah River Plant, near Aiken, SC, are exposed to large temperature fluctuations resulting from reactor operations. Rates of primary production and species composition were monitored at 4 sites along a thermal gradient in a trough microcosm to determine how these large temperature fluctuations affected productivity and algal community structure. Blue-green algae (cyanobacteria) were the only phototrophic primary producers growing in water above 45°C. These thermophiles were able to survive and apparently adapt to ambient temperatures when the reactor was shut down. The algal mat communities exposed to <45°C were composed of blue-green and eukaryotic algae that adapted rapidly to ambient temperatures. An increase in the percentage extracellular release (PER) of¹⁴C-labeled dissolved organic compounds and a decrease in primary production were observed during periods of thermal fluctuation. The results show that the dominant phototrophs in this artificially heated aquatic habitat have been selected for their ability to survive large temperature fluctuations and are similar to those of natural hot springs.This paper was prepared in connection with work under Contract No. DE-AC09-76SR00001 with the U.S. Department of Energy.     

Influence of the Thin Drift Algal Mats on the Distribution of Macrozoobenthos in Kõiguste Bay, NE Baltic Sea

Macrozoobenthic communities within and outside of the drift algal mats were compared in Kõiguste Bay, NE Baltic Sea. The patches of the drift algae were on average 0.5–1 km wide in diameter covering about 25% of the total bottom area of the bay. Thickness of the mat did not exceed 6 cm. The biomass of the mat varied between 35 and 1391 g dw m^?2. The drift algal mats had no clear negative effect on macrozoobenthos except for a few infaunal species. The drift algae favoured several detrivorous, herbivorous and carnivorous species. Among the studied variables, the thickness of algal mat and oxygen concentration at near-bottom layer explained the best the structure of macrozoobenthos. Total number of invertebrate species increased curvilinearly with the thickness of algal mat having the peak value at 3–5 cm thick algal mat. To conclude, moderate drift algal mats increased habitat complexity and, thus, the diversity of benthic faunal assemblages in otherwise poorly vegetated coastal areas.     

The characterization of the RNAs and aminoacyl-tRNA synthetases of the blue-green alga, Anacystis nidulans

The tRNA and aminoacyl-tRNA synthetases of the blue-green alga, Anacystis nidulans have been isolated and studied. The distribution of some algal tRNA species on BD-cellulose chromatography has been determined. One tRNA^Met species has been isolated in 80% purity by a single chromatography on a BD-cellulose column developed with a modified salt gradient. The number of different tRNA isoacceptors for Met, Ser, and Leu has been ascertained by RPC-5 chromatography. The recognition of algal tRNAs by the homologous algal synthetase preparation as well as the heterologous Escherichia coli preparation was studied by the aminoacylation tests. Since all of the isoaccepting species of the tRNAs tested behaved almost identically in presence of the two enzyme preparations, a conservation of the recognition site during the evolutionary divergence of bacteria and algae is strongly suggested.     

Meteorological effects on variation of airborne algae in Mexico

Sixteen species of algae were collected from 73.8 m³ of air. Eleven were obtained in Minatitlán and eleven in México City. The data show that similar diversity occurred between the two localities, in spite of the difference in altitude. This suggests that cosmopolitan airborne microorganisms might have been released from different sources. Three major algal divisions (Chlorophyta, Cyanophyta and Chrysophyta) formed the airborne algal group. Also, a large concentration of 2220 algae m^–3 was found near sea-level, while lower amounts were recorded at the high altitude of México City. The generaScenedesmus, Chlorella andChlorococcum dominated. Striking relationships were noted between the concentration of airborne green and blue-green algae, and meteorological conditions such as rain, vapour pressure, temperature and winds for different altitudes. In Minatitlán a linear relationship was established between concentration of algae and both vapour pressure (mbar) and temperature (° C), while in México City the wind (m s^–1) was associated with variations in the algal count.     

Fairy, tadpole, and clam shrimps (Branchiopoda) in seasonally inundated clay pans in the western Mojave Desert and effect on primary producers

Background

Fairy shrimps (Anostraca), tadpole shrimps (Notostraca), clam shrimps (Spinicaudata), algae (primarily filamentous blue-green algae [cyanobacteria]), and suspended organic particulates are dominant food web components of the seasonally inundated pans and playas of the western Mojave Desert in California. We examined the extent to which these branchiopods controlled algal abundance and species composition in clay pans between Rosamond and Rogers Dry Lakes. We surveyed branchiopods during the wet season to estimate abundances and then conducted a laboratory microcosm experiment, in which dried sediment containing cysts and the overlying algal crust were inundated and cultured. Microcosm trials were run with and without shrimps; each type of trial was run for two lengths of time: 30 and 60 days. We estimated the effect of shrimps on algae by measuring chlorophyll content and the relative abundance of algal species.

Results

We found two species of fairy shrimps (Branchinecta mackini and B. gigas), one tadpole shrimp (Lepidurus lemmoni), and a clam shrimp (Cyzicus setosa) in our wet-season field survey. We collected Branchinecta lindahli in a pilot study, but not subsequently. The dominant taxa were C. setosa and B. mackini, but abundances and species composition varied greatly among playas. The same species found in field surveys also occurred in the microcosm experiment. There were no significant differences as a function of experimental treatments for either chlorophyll content or algal species composition (Microcoleus vaginatus dominated all treatments).

Conclusions

The results suggest that there was no direct effect of shrimps on algae. Although the pans harbored an apparently high abundance of branchiopods, these animals had little role in regulating primary producers in this environment.     

Biological activity of l-2-azetidinecarboxylic acid,isolated from Polygonatum odoratum var. pluriflorum, against several algae

The biological activities of an aqueous fraction extracted from Polygonatum odoratum var. pluriflorum Owhi and of l-2-azetidinecarboxylic acid (AZC), purified from the extract, on the growth of several types of algae were tested. The aqueous fraction was prepared by methanol extraction of P. odoratum var. pluriflorum rhizomes followed by reverse partitioning with butanol. The aqueous extraction inhibited growth of the green alga Chlorella vulgaris by less than 10% at a concentration of 1000 mg L⁻¹. However, growth of the blue-green alga Microcystis aeruginosa was inhibited by 22.0%, 67.9%, and 87.1%, respectively, at 3.1, 6.2, and 12.5 mg extract L⁻¹. AZC was isolated from the aqueous extract and was shown to be the major active substance inhibiting algal growth. AZC concentrations higher than 25 μM inhibited growth, while at 400 μM, growth of the green algae C. vulgaris and Scenedesmus spp. was inhibited by 71.2% and 70.4%, respectively. In contrast, growth of the blue-green algae Anabaena affinis and M. aeruginosa was inhibited at concentrations greater than 1.6 and 0.2 μM, respectively, whereas 92% control required concentrations of 6.3 and 1.6 μM, respectively. AZC also suppressed the growth of the red-tide microalga Cochlodinium polykrikoides by 86.9% and 100% at concentrations of 6.3 and 12.5 μM, respectively. Azetidine and 2-azetidinone showed little activity on the tested algae. The results demonstrate that AZC selectively inhibits algal growth at low concentrations. The green algae C. vulgaris and Scenedesmus spp. were tolerant, whereas M. aeruginosa, A. affinis, and C. polykrikoides were relatively sensitive. Thus, extract and AZC, prepared from P. odoratum rhizomes, showed a potential as natural selective algicide for the control of harmful algae in laboratory assay.     

Seasonal succession of the phytoplankton in the upper Mississippi River

Species composition and seasonal succession of the phytoplankton were investigated on the upper Mississippi River at Prairie Island, Minnesota, U.S.A. Both the numbers and volume of individual species were enumerated based on cell counts with an inverted microscope. A succession similar to algal succession in the local lakes occurred. The diatoms were dominant during the spring and fall and blue-green algae were dominant during the summer. The algal concentrations have increased up to 40 fold the concentrations of the 1920's, since the installation of locks and dams. The maximum freshweight standing crop was 4 mg · l^–1 in 1928 (Reinhard 1931), 13 mg · l^–1 in 1975 a wet year, and 47 mg · l^–1 in 1976, a relatively dry year with minimal current discharge. The diatoms varied from 36–99%, the blue-green algae from 0–44% and the cryptómonads from 0–50% of the total standing crop. The green algae were always present but never above 21% of the biomass. The dominant diatoms in recent years were centric -Stephanodiscus andCyclotella spp. (maximum 50,000 ml^–1). The dominant blue-green algae wereAphanizomenon flos-aquae (L.) Ralfsex Born.et Flahault andOscillatoria agardhii Gomont (maximum 800 ml^–1). These algal species are also present in local lakes. Shannon diversity values indicated greatest diversity of algae during the summer months.     

Lytic Organisms and Photooxidative Effects: Influence on Blue-Green Algae (Cyanobacteria) in Lake Mendota, Wisconsin

The effects of exposure to high light intensities on blue-green algal (cyanobacterial) populations were examined in Lake Mendota, Wis. The algal populations were shown to be susceptible to inhibition of photosynthetic activity and pigment bleaching as a result of exposure. These effects generally influence only a small percentage of the lake population and thus are probably not important in causing major declines in chlorophyll a. Lytic organisms were shown to increase in numbers in the lake in response to the seasonal development of blue-green algae, reaching values of greater than 1,000 plaque-forming units per ml in midsummer. Both bacteria and protozoa were observed in plaque zones, but it could not be determined whether these lytic organisms had a major role in algal biomass declines.     

Functional structure of algal mat (Cladophora glomerata) in a freshwater in western Poland

GAMs (Generalized Additive Models) present a growth pattern for the common filamentous algae (FA) taxa in freshwater ecosystems in Poland. Tribonema, Ulothrix taxa are an early spring species. In comparison with Rhzioclonium, Cladophora and Oedogonium taxa, the algae Zygnemataceae (e.g. Zygnema, Spirogyra) occurs in waters with lower levels of nutrients, total dissolved substances and electrical conductivity. Cladophora glomerata shows different responses to environmental gradients than C. rivularis, C. fracta. Furthermore, the algae Cladophora glomerata (Chlorophyta, Ulvophyceae) forms a thick monoalgae mat (from the surface to the bottom) in the shallow and eutrophic Lake Oporzynskie in Wielkopolska Region in Poland (Central Europe). Detailed algal mat characteristics, physical and chemical parameters of water, and pigments in thalli were measured vertically (surface, middle, bottom) and spatially (marginal and central part) in the stationary mat phase during maximal algal growth. Temperature, dissolved oxygen and PAR irradiation significantly declined as the depth of the mat increased. Water turbidity was greater in the surface layer than in deeper parts, in contrast to the concentrations of N-NO₃, N-NH₄ and TDS. Pigment content in the cells of C. glomerata, cell lengths and diameters of pyrenoids changed throughout the mat, from top to bottom. The obtained data were used for statistical analyses. In conclusion: dense mats of C. glomerata show a vertical stratification while the mats remain spatially homogenous. Our data suggest that mat structure be considered a biological indicator of freshwater eutrophication.     

Concentration of 137Cs, 65Zn,and 85Sr by fresh-water algae

Differences in the concentration and retention of ¹³⁷Cs by unicellular diatoms, filamentous green algae, and filamentous blue-green algae were demonstrated under both batch and continuous-flow culture conditions. ¹³⁷Cs concentration factors were generally higher by a factor of 2 in batch tests than in continuous flow tests. In retention studies, ¹³⁷Cs was desorbed more rapidly from algae under continuous-flow conditions. Studies with blue-green algae indicate that ¹³⁷Cs concentrations in the various species were more closely related to the surface-to-volume ratios of algal cells than to the systematic relationships of the three species. Continuous-flow studies indicated no differences among three species of filamentous green algae in the concentration of ¹³⁷Cs, ⁶⁵Zn, and ⁸⁵Sr. However, the average concentration factors of the radionuclides were considerably different: 3800 for ⁶⁵Zn, 460 for ¹³⁷Cs, and 230 for ⁸⁵Sr. These radionuclides were rapidly desorbed following the transfer of algae to nonradioactive media. The desorption rate was inversely related to the concentration rate.